1. Technical Field of the Invention
The present invention relates generally to digital power supplies and, more particularly, to a pulse width modulated (PWM) timer for use in a digital power supply.
2. Description of Related Art
Forward power converters are well known in the art. These converters include a plurality of transistors each with a control terminal. Control signals are supplied to the control terminals with a certain relationship to each other in order to properly operate the converter. It is critical that the timing of operation of the transistors be carefully controlled. Timing circuits of varying types have been used to generate the control signals.
For example, the STM32 MCU from STMicroelectronics has been used to generate the control signals in a power converter application. The STM32 device is designed and optimized for three-phase motor control. As such, the circuit architecture is configured to control a three-phase bridge, and more specifically to control three half bridges. This bridge architecture shares some similarities with the power converter architecture, and further shares some PWM control similarities with power converter circuits.
While a motor controller needs to control only two transistors in a half bridge, the control operation for a power converter is more complex. In a single phase power converter, for example, two transistors must be controlled on the primary side, and one or more additional transistors must be controlled on the secondary side in order to achieve synchronous rectification. In addition, if one desires to implement current control in addition to voltage control, one of the controlled switching events in the power converter must be triggered by a current detection (and not by the digital PWM generator).
To address the power converter control and timing needs, the timers provided by the STM32 MCU have been used to generate the transistor control signals. However, because the STM32 is designed for motor control and not power converter control, the use of the STM32 as the power converter control circuit is not optimized. A need exists for a control circuit having optimized timers. Such a control circuit should support the use of programmable delays between the transistor control signals.